Typical for me...I'm WAY overthinking this already!!
I have imagined an "accidental discharge" so thought of possibly mounting the extinguisher INSIDE a piece of PVC pipe with a screw on cap. Or mounting it with a safety device that shields the pin and lever....a bit like the way GI hand grenades or smoke grenades are shipped.
I carry a 2.5# dry chem in the pannier of my BMW GS. Four years ago in Nevada I came upon a guy on a Harley that had leaked fuel from the lower tank fitting*, he had stopped and the bike ignited. Luckily I was less than 100 yds away....and already slowing when it ignited. We were able to keep it out long enough to crimp the fuel line with a Leathermen. It reignited, and I put it out again. We both had water and doused it with that...which helped as well.
The 2.5# was enough THAT time anyway.
* He had filled the bike with DIESEL some miles back, then removed the fitting to drain the tank. Two hours of fooling around with draining the diesel, flushing the tank, fuel into the FI, running the battery down...after a couple of jump starts it fiinally starts.
He goes about twenty miles and smells fuel...stops and WOOSH!
A new rider, out for his firsat big bike adventure. Well...he surely had one.
FN